Seamless Network-Wide IGP Migrations Laurent Vanbever, Stefano Vissicchio, Cristel Pelsser, Pierre Francois, and Olivier Bonaventure laurent.vanbever@uclouvain.be SIGCOMM August 18, 2011
It is not the strongest of the species that survives, nor the most intelligent. — Leon Megginson (miss-attributed to Darwin)
It is not the strongest of the species that survives, nor the most intelligent. It is the one that is most adaptable to change. — Leon Megginson (miss-attributed to Darwin)
Last week on the NANOG mailing-list ... Is there any reason to run IS-IS over OSPF in the service provider core? Currently, we are running IS-IS but we are redesigning our core and now would be a good time to switch. I would like to switch to OSPF, mostly because of familiarity with OSPF over IS-IS. What does everyone think? NANOG thread, OSPF vs IS-IS , 11/08/11
Migrating the IGP is about network-wide reconfiguration How do we get from here ... IS-IS Area 49.0000 L2 L2 L2 L2 10 1 10 3 3 100 4 4 100 3 3 1 10 10 L2 L2 L2 L2
Migrating the IGP is about network-wide reconfiguration ... to there ? ABR ABR 10 1 10 3 3 100 4 4 100 Backbone 3 3 Router 1 1 10 10 ABR ABR OSPF OSPF OSPF Area 0.0.0.1 Area 0.0.0.2 Area 0.0.0.0
Reconfiguring the IGP can provide immediate benefits to the network IGP reconfigurations can improve the manageability performance stability security of the entire network
Migrating the IGP is operationally complex Reconfigure a running network while respecting Service Level Agreement Make highly distributed changes on all the routers, in a coordinated manner Face potential routing anomalies as non-migrated routers interact with migrated ones
Current approaches do not entirely solve the problem Reconfigure weights/links Disruption free topology reconfiguration [Francois et al. INFOCOMM’2007] Loop-free updates of forwarding tables [Fu et al. IEEE TNSM 2008, Shi et al. ICC’2009] Graceful Network Operations [Raza et al. INFOCOMM’2009] Modify the routers Shadow Configuration [Alimi et al. SIGCOMM’2008] Take advantage of virtualization VROOM [Wang et al. SIGCOMM’2008] BGP Grafting [Keller et al. NSDI’2010]
Problem Replace the anomaly-free IGP configuration of a running network, router-by-router, without causing any routing anomalies
Sub-problem 1 Replace the anomaly-free IGP configuration of a running network, router-by-router, without causing any routing anomalies Current Run the two IGP configurations in parallel Practice
Migrating the IGP usually requires running two routing planes Abstract model of a router At first, the initial IGP dictates the forwarding Control-plane Initial IGP paths being used Initial Data-plane Forwarding paths
Migrating the IGP usually requires running two routing planes Abstract model of a router Then, the final IGP is introduced without Control-plane Initial IGP Final IGP changing the forwarding Initial Data-plane Forwarding paths
Migrating the IGP usually requires running two routing planes Abstract model of a router After having converged, the final IGP is used by Control-plane Initial IGP Final IGP flipping the preference Final Data-plane Forwarding paths
Migrating the IGP usually requires running two routing planes Abstract model of a router After having converged, the final IGP is used by Control-plane Initial IGP Final IGP flipping the preference | M I G R Final A T Data-plane Forwarding paths E D |
Migrating the IGP usually requires running two routing planes Abstract model of a router The initial IGP is removed Control-plane Final IGP as it is not used anymore | M I G R Final A T Data-plane Forwarding paths E D |
Sub-problem 1 Replace the anomaly-free IGP configuration of a running network, router-by-router, without causing any routing anomalies
Sub-problem 2 Replace the anomaly-free IGP configuration of a running network, router-by-router, without causing any routing anomalies
Migrating the IGP can create migration loops Tested networks 1 (cumul. frequency) flat2hier A lot of networks experience loops 0 0 # possible loops 90 Up to 90 migration loops can arise during an IGP migration
Sub-problem 2 Replace the anomaly-free IGP configuration of a running network, router-by-router, without causing any routing anomalies
Sub-problem 2 Replace the anomaly-free IGP configuration of a running network, router-by-router, without causing any routing anomalies Contributions Seamless IGP migration is possible as long as the reconfiguration process follows a strict ordering
Contributions Seamless IGP migration is possible as long as the reconfiguration process follows a strict ordering which one ?
Contributions 1. Seamless IGP migration is possible as long as the reconfiguration process follows a strict ordering
Contributions 1. Seamless IGP migration is possible as long as the reconfiguration process follows a strict ordering 2. Decide if an ordering exists is NP-complete
Contributions 1. Seamless IGP migration is possible as long as the reconfiguration process follows a strict ordering 2. Decide if an ordering exists is NP-complete 3. Develop an exponential algorithm as well as a heuristic to compute the ordering
Contributions 1. Seamless IGP migration is possible as long as the reconfiguration process follows a strict ordering 2. Decide if an ordering exists is NP-complete 3. Develop an exponential algorithm as well as a heuristic to compute the ordering 4. Provide fallback solutions when no ordering exists
Contributions 1. Seamless IGP migration is possible as long as the reconfiguration process follows a strict ordering 2. Decide if an ordering exists is NP-complete 3. Develop an exponential algorithm as well as a heuristic to compute the ordering 4. Provide fallback solutions when no ordering exists 5. Outline solutions for link failures and congestion
Seamless IGP migration is possible as long as the reconfiguration process follows a strict ordering which one ?
Seamless Network-Wide IGP Migrations Identify the ordering 1 Avoid anomalies Compute the ordering 2 Manage complexity Apply the ordering 3 Stable, efficient
Seamless Network-Wide IGP Migrations 1 Identify the ordering Avoid anomalies Compute the ordering Manage complexity Apply the ordering Stable, efficient
Reconfiguring the IGP might change the forwarding paths being used In a flat IGP, routers forward traffic according to the shortest-path towards the destination. In a flat IGP, R4 reaches R1 via R3 10 1 10 R1 R3 R5 R7 100 4 1 100 R2 R4 R6 R8 10 3 10
Reconfiguring the IGP might change the forwarding paths being used In a hierarchical IGP, routers prefer paths contained within a single zone over the ones crossing several zones In a hierarchical IGP, R4 reaches R1 via R2 10 1 10 R1 R3 R5 R7 100 4 1 100 Zone A Backbone Zone B R2 R4 R6 R8 10 3 10
Whenever the forwarding paths change, forwarding loops can be created initial paths final paths R1 R3 R1 R3 10 10 100 1 100 1 10 10 R2 R4 R2 R4 flat IS-IS hierarchical OSPF Forwarding paths towards R1
initial paths intermediate paths final paths R1 R3 R1 R3 R1 R3 10 10 10 100 1 100 1 100 1 10 10 10 R2 R4 R2 R4 R2 R4 flat IS-IS hierarchical OSPF Forwarding paths towards R1
First, we migrate R3 initial paths intermediate paths final paths R1 R3 R1 R3 R1 R3 10 10 10 100 1 100 1 100 1 10 10 10 R2 R4 R2 R4 R2 R4 flat IS-IS hierarchical OSPF Forwarding paths towards R1
First, we migrate R3 initial paths intermediate paths final paths R1 R3 R1 R3 R1 R3 10 10 10 100 1 100 1 100 1 10 10 10 R2 R4 R2 R4 R2 R4 flat IS-IS hierarchical OSPF Forwarding paths towards R1
Then, we migrate R4 initial paths intermediate paths final paths R1 R3 R1 R3 R1 R3 10 10 10 100 1 100 1 100 1 10 10 10 R2 R4 R2 R4 R2 R4 flat IS-IS hierarchical OSPF Forwarding paths towards R1
Then, we migrate R4 initial paths intermediate paths final paths R1 R3 R1 R3 R1 R3 10 10 10 100 1 100 1 100 1 10 10 10 R2 R4 R2 R4 R2 R4 flat IS-IS hierarchical OSPF Forwarding paths towards R1
Whenever the forwarding paths change, forwarding loops can be created A loop is created if R4 is migrated before R2 initial paths intermediate paths final paths R1 R3 R1 R3 R1 R3 10 10 10 100 1 100 1 100 1 10 10 10 R2 R4 R2 R4 R2 R4 flat IS-IS hierarchical OSPF Forwarding paths towards R1
Migrations have to be performed following a precise ordering No loop arises if R2 is migrated before R4 initial paths intermediate paths final paths R1 R3 R1 R3 R1 R3 10 10 10 100 1 100 1 100 1 10 10 10 R2 R4 R2 R4 R2 R4 flat IS-IS hierarchical OSPF Forwarding paths towards R1
Migrations have to be performed following a precise ordering No loop arises if R2 is migrated before R4 initial paths intermediate paths final paths R1 R3 R1 R3 R1 R3 10 10 10 100 1 100 1 100 1 10 10 10 R2 R4 R2 R4 R2 R4 flat IS-IS hierarchical OSPF Forwarding paths towards R1
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